84 research outputs found
An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?
High energy observations of extreme BL Lac objects, such as 1ES 0229+200 or
1ES 0347-121, recently focused interest both for blazar and jet physics and for
the implication on the extragalactic background light and intergalactic
magnetic field estimate. However, the number of these extreme highly peaked BL
Lac objects (EHBL) is still rather small. Aiming at increase their number, we
selected a group of EHBL candidates starting from the BL Lac sample of Plotkin
et al. (2011), considering those undetected (or only barely detected) by the
Large Area Telescope onboard Fermi and characterized by a high X-ray vs. radio
flux ratio. We assembled the multi-wavelength spectral energy distribution of
the resulting 9 sources, profiting of publicly available archival observations
performed by the Swift, Galex and Fermi satellites, confirming their nature.
Through a simple one-zone synchrotron self-Compton model we estimate the
expected VHE flux, finding that in the majority of cases it is within the reach
of present generation of Cherenkov arrays or of the forthcoming Cherenkov
Telescope Array (CTA).Comment: 12 pages, 5 figures, accepted for publication in MNRA
Very-high-energy quasars hint at ALPs
One of the mysteries of very-high-energy (VHE) astrophysics is the
observation of flat spectrum radio quasars (FSRQs) above about 30 GeV, because
at those energies their broad line region should prevent photons produced by
the central engine to escape. Although a few astrophysical explanations have
been put forward, they are totally ad hoc. We show that a natural explanation
emerges within the conventional models of FSRQs provided that photon-ALP
oscillations take place inside the source for the model parameters within an
allowed range.Comment: 4 pages, 3 figures. Proceeding of the workshop "9th Patras Workshop
on Axions, WIMPs and WISPs", 24 - 28 June 2013, Schloss Waldhausen, Mainz,
Germany (to be published in the Proceedings
Blazars distance indications from Fermi and TeV data
A new method to constrain the distance of blazars with unknown redshift using
combined observations in the GeV and TeV regimes will be presented. The
underlying assumption is that the Very High Energy (VHE) spectrum corrected for
the absorption of TeV photons by the Extragalactic Background Light (EBL) via
photon-photon interaction should still be softer than the extrapolation of the
gamma-ray spectrum observed by Fermi/LAT. Starting from the observed spectral
data at VHE, the EBL-corrected spectra are derived as a function of the
redshift z and fitted with power laws. Comparing the redshift dependent VHE
slopes with the power law fits to the LAT data an upper limit to the source
redshift can be derived. The method is applied to all TeV blazars detected by
LAT with known distance and an empirical law describing the relation between
the upper limits and the true redshifts is derived. This law can be used to
estimate the distance of unknown redshift blazars: as an example, the distance
of PKS 1424+240 is inferred.Comment: Contribution to SciNeGHE 2010, Trieste, Italy, September 2010; 4
pages, 2 figur
TeV blazars and their distance
Recently, a new method to constrain the distance of blazars with unknown
redshift using combined observations in the GeV and TeV regimes has been
developed, with the underlying assumption that the Very High Energy (VHE)
spectrum corrected for the absorption of TeV photons by the Extragalactic
Background Light (EBL) via photon-photon interaction should still be softer
than the gamma-ray spectrum observed by Fermi/LAT. The constraints found are
related to the real redshifts by a simple linear relation, that has been used
to infer the unknown distance of blazars. The sample will be revised with the
up-to-date spectra in both TeV and GeV bands, the method tested with the more
recent EBL models and finally applied to the unknown distance blazars detected
at VHE.Comment: Contribution to "Cosmic Radiation Fields: Sources in the early
Universe", Desy, Germany, November 9-12, 2010; 6 pages, 3 figures (revised
version
Boosting the performance of the ASTRI SST-2M prototype: reflective and anti-reflective coatings
ASTRI is a Flagship Project of the Italian Ministry of Education, University
and Research, led by the Italian National Institute of Astrophysics, INAF. One
of the main aims of the ASTRI Project is the design, construction and
verification on-field of a dual mirror (2M) end-to-end prototype for the Small
Size Telescope (SST) envisaged to become part of the Cherenkov Telescope Array.
The ASTRI SST-2M prototype adopts the Schwarzschild-Couder design, and a camera
based on SiPM (Silicon Photo Multiplier); it will be assembled at the INAF
astronomical site of Serra La Nave on mount Etna (Catania, Italy) within mid
2014, and will start scientific validation phase soon after. The peculiarities
of the optical design and of the SiPM bandpass pushed towards specifically
optimized choices in terms of reflective coatings for both the primary and the
secondary mirror. In particular, multi-layer dielectric coatings, capable of
filtering out the large Night Sky Background contamination at wavelengths
nm have been developed and tested, as a solution for the
primary mirrors. Due to the conformation of the ASTRI SST-2M camera, a
reimaging system based on thin pyramidal light guides could be optionally
integrated aiming to increase the fill factor. An anti-reflective coating
optimized for a wide range of incident angles faraway from normality was
specifically developed to enhance the UV-optical transparency of these
elements. The issues, strategy, simulations and experimental results are
thoroughly presented.Comment: 4 pages, 6 figures. In Proceedings of the 33rd International Cosmic
Ray Conference (ICRC2013), Rio de Janeiro (Brazil). All ASTRI contributions
at arXiv:1307.463
Calibration of the ASTRI SST-2M Prototype using Muon Ring Images
The study of ring images generated from high-energy muons is a very useful
tool for the performance monitoring and calibration of any Imaging Atmosphere
Cherenkov Telescope. Isolated muons travelling towards the telescope light
collector system produce characteristic Cherenkov ring images in the focal
plane camera. Since the geometry and the distribution of light deployed onto
the camera can be easily reconstructed analytically for a muon of given energy
and direction, muon rings are a powerful tool for monitoring the behaviour of
crucial properties of an imaging telescope such as the point-spread-function
and the overall light collection efficiency. In this contribution we present
the possibility of using the analysis of muon ring images as calibrator for the
ASTRI SST-2M prototype point spread function.Comment: In Proceedings of the 33rd International Cosmic Ray Conference
(ICRC2013), Rio de Janeiro (Brazil). All ASTRI contributions at
arXiv:1307.463
The mini-array of ASTRI SST-2M telescopes, precursors for the Cherenkov Telescope Array
In the framework of the Cherenkov Telescope Array (CTA) Observatory, the Italian National Institute of Astrophysics (INAF) has recently inaugurated in Sicily (Italy), at the Serra La Nave astronomical site on the slopes of Mount Etna, a large field of view (FoV, ∼ 9.6°) dual-mirror prototype (ASTRI SST-2M) of the CTA small size class of telescopes (SST). The CTA plans to install about 70 SST in the southern site to allow the study of the gamma rays from a few TeV up to hundreds of TeV. The ASTRI SST-2M telescope prototype has been developed following an end-to-end approach, since it includes the entire system of structure, mirrors optics (primary and secondary mirrors), camera, and control/acquisition software. A remarkable performance improvement could come from the operation of the ASTRI mini-array, led by INAF in synergy with the Universidade de Sao Paulo (Brazil) and the North-West University (South Africa). The ASTRI mini-array will be composed of nine ASTRI SST-2M units and it is proposed as a precursor and initial seed of the CTA to be installed at the final CTA southern site. Apart from the assessment of a number of technological aspects related to the CTA, the ASTRI mini-array will, if compared for instance to H.E.S.S., extend the point source sensitivity up to ∼ 100 TeV, also improving it above 5-10 TeV. Moreover, the unprecedented width of the FoV, with its homogeneous acceptance and angular resolution, will significantly contribute to the achievement of original results during the early CTA science phase
Calibration of the ASTRI SST-2M Prototype using Muon Ring Images
The study of ring images generated from high-energy muons is a very useful tool for the performance monitoring and calibration of any Imaging Atmosphere Cherenkov Telescope. Isolated muons travelling towards the telescope light collector system produce characteristic Cherenkov ring images in the focal plane camera. Since the geometry and the distribution of light deployed onto the camera can be easily reconstructed analytically for a muon of given energy and direction, muon rings are a powerful tool for monitoring the behaviour of crucial properties of an imaging telescope such as the point-spread-function and the overall light collection efficiency. In this contribution we present the possibility of using the analysis of muon ring images as calibrator for the ASTRI SST-2M prototype point spread function
MAGIC observations of Mkn 421 in 2008, and related optical/X-ray/TeV MWL study
The HBL-type blazar Markarian 421 is one of the brightest TeV gamma-ray
sources of the Northern sky. From December 2007 until June 2008 it was
intensively observed in the VHE (E>100 GeV) band by the MAGIC gamma-ray
telescope. The source showed intense and prolonged activity during the whole
period. In some nights the integral flux rose up to 3.6 Crab units (E>200 GeV).
Intra-night rapid flux variations were observed. We compared the optical (KVA)
and X-ray (RXTE-ASM, Swift-XRT) data with the MAGIC VHE data, investigating the
correlations between different energy bands.Comment: 4 pages,4figures, Contribution to the 31st ICRC, Lodz, Poland, July
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